The present application is generally related to stimulation systems, for example, spinal cord, peripheral, deep-brain, and cortical stimulation systems. A spinal cord stimulation system is an implantable pulse generating system used to provide electrical stimulation pulses to an electrode array placed epidurally or surgically near a patient's spine. An implanted pulse generator (IPG) may operate independently to provide the required electrical stimulation, or may interact with an external programmer, which delivers programming, control information, and/or energy for the electrical stimulation, typically through a radio-frequency (RF) or other wireless signal.
Spinal cord stimulation (SCS) is a well accepted clinical method for reducing pain in certain populations of patients. SCS systems typically include an implanted device, lead wires, and electrodes connected to the lead wires. The implanted device receives signals from an external programmer, and transmits corresponding electrical pulses that are delivered to the spinal cord (or other tissue) through the electrodes which are implanted along the dura of the spinal cord. In a typical situation, the attached lead wires exit the epidural space and are tunneled around the torso of the patient to a subcutaneous pocket where the device is implanted.
Spinal cord and other stimulation systems are known in the art. For example, U.S. Pat. No. 3,646,940 discloses an implantable electronic stimulator that provides timed sequenced electrical impulses to a plurality of electrodes so that only one electrode has a voltage applied to it at any given time. Thus, the electrical stimuli provided by the apparatus taught in the '940 patent comprise sequential, or non-overlapping, stimuli.
U.S. Pat. No. 3,724,467 discloses a relatively thin and flexible strip of physiologically inert plastic with a plurality of electrodes formed thereon for stimulation of the spinal cord. The electrodes are connected by leads to an RF receiver, which is also implanted, and which is controlled by an external controller. The implanted RF receiver has no power storage means for generating electrical stimulations and must be coupled to the external controller in order for neurostimulation to occur.
U.S. Pat. No. 3,822,708 discloses another type of electrical spinal cord stimulating device. The device has five aligned electrodes which are positioned longitudinally on the spinal cord and transversely to the nerves entering the spinal cord. Current pulses applied to the electrodes are said to block sensed intractable pain, while allowing passage of other sensations. The stimulation pulses applied to the electrodes are approximately 250 microseconds in width with a repetition rate of 5 to 200 pulses per second. A patient-operable switch allows the patient to change which electrodes are activated, i.e., which electrodes receive the current stimulus, so that the area between the activated electrodes on the spinal cord can be adjusted, as required, to better block the pain.
Other representative patents that show spinal cord stimulation systems or electrodes include U.S. Pat. Nos. 4,338,945; 4,379,462; and 4,793,353. All of the patents noted above are hereby incorporated by reference.
A typical IPG is self contained, having a multi-year battery pack and a single treatment program, and is generally programmed during or immediately following implantation in the patient's body. The battery may be rechargeable or non-rechargeable.
Other SCS systems have no implanted power source, but receive power and programming and/or control information from an external transmitter. These systems will convert the RF signals from the transmitter to provide power to the implanted receiver, and use the RF programming information to determine the intensity, location, and duration of the electrical pulses delivered to the electrodes.
Programming SCS systems is a relatively complicated process. At a high level, programming an SCS system involves selecting stimulation parameters (pulse amplitude, pulse width, pulse frequency, an electrode combination) that are effective in addressing the pain pattern of a patient. In some cases, the patient may experience pain in multiple distinct regions of the patient's body. In such cases, a stimulation “program” can be created to include multiple “stimsets” that are each adapted to address pain in a specific, discrete region of the body.
During an initial or follow-up programming session, stimulation programs may be generated in a somewhat “piecemeal” manner. Specifically, the stimsets are each constructed individually by downloading the stimsets from a patient programmer device to an IPG and observing the response of the patient. The parameters are varied for an individual stimset until a satisfactory stimulation response for a particular region of the patient's body is obtained. Once all of the stimsets are defined in this manner, the stimsets are combined into a stimulation program which is downloaded to the IPG. The stimulation program causes a pulse generator to repeatedly generate pulses in rapid succession according to the respective stimsets. The goal of a stimulation program in SCS is to cause the patient to subjectively experience pain relief for all of the affected regions in a simultaneous manner.